Stable fluorophosphate optical glass

ABSTRACT

Fluoro-phosphate optical glass having an extremely low tendency to devitrify, a high water-durability and a low brittleness is produced by incorporation boron oxide in the binary system phosphoric anhydride-metal fluorides, wherein said metal fluorides consists of alkaline earth metal fluorides such as MgF2, BaF2 and CaF2, and aluminum fluoride with or without alkali metal fluoride or fluorides.

MEMO 1 lzumitani et a1.

[151 mamas [451 Apr. 10, 1072 I [54] STABLE FLUOROPHOSPTE OPTICAL GLASS [72] Inventors: Tetsuro Izumitani, Tokyo; Seiichi Toda,

- I-Ianno, both ofJapan' [73] Assignee: I-Iaya Glass Works, Limited, Tokyo, Japan [22] Filed: I May 15, 1970 [21] Appl. No.: 37,763

[30] Foreign Application Priority Data 2,511,228 6/1950 Sunetal...' ..106/47Q 2,456,033 12/1948 Sun.- ..l06/47 Q FOREIGN PATENTS OR APPLICATIONS 909,679 10/1962 Great Britain ..106/47 Q OTHER PUBLICATIONS Rawson, I-I.; Inorganic Glass Forming Systems; London, 1967,

' p. 173 (TP857R3) Primary Examiner--Tobias E. Levow Assistant Examiner-W. R. Satterfield Att0rney--Cushman, Darby & Cushman [57] ABSTRACT Fluoro-phosphate optical glass having an extremely low tendency to devitrify, a high water-durability and a low brittleness is produced by incorporation boron oxide in the binary system phosphoric anhydride-metal fluorides, wherein said metal fluorides consists of alkaline earth metal fluorides such as MgF Hal-' and Cal-' and aluminum fluoride with or without alkali metal fluoride or fluorides.

4 Claims, 3 Drawing Figures PmENTEnAPmm 3,656,976

SHEET 10F 3 'GLASS FORMING REGION PMENTEDAPR 18 I972 3. 656, 976 SHEET 2 OF 3 CATIONIC PERFECTLY STABLE GLASS FORMING REGION GLASS FORMING REGION BcFe C JF2 I N F|O% -PzOs 20% PATENTED PRHHHYE I 3,656,976

YSHEET3DF3 MgFz CATIONIC /o FIG. 3

PERFECTLY STABLE GLASS FORMING REGION Cu F2 GLASS FERMING REGION v ALF320% STABLE FLUOROPI-IOSPI-IATE OPTICAL GLASS The present invention relates to optical glass, and more particularly, to an fluorophosphate glass which is improved as to devitrification, water-durability and brittleness.

There have been produced heretofore optical glass having a Therefore, an object of the present invention is to provide a.

fluorophosphate glass which is stable so as to have a low tendency to devitrify and which has a high water durability.

Anotherobject of the present invention is to provide a fluorophosphate' glass which is not subject to the propagation of crack.

Still another object of the present invention is to providesuch a glass suitable for a mass production.

In the following description of the present invention,. reference is made to the Figures of accompanying drawings, in

which:

FIG. 1 represents a glass forming region and a perfectly stable glass forming region in the ternary system /2 RO A B -Me(F) when Me(F) is a mixture consisting by cationic part of 15 parts of NaF, 23 parts of AlF 10 parts of MgF 14 parts of Bal and 18 parts of CaF FIG. 2 represents those regions in the same ternary system: when /2 P 0 AlF and NaF are by cationic percent 20, 17.5'

and respectively; and

FIG. 3 represents similarly those regions in the same ternary system, when V; P 0 AlF and NaF are by cationic percent 35, 20 and 10 respectively.

The present inventors have discovered that in the A: P,o,- /2

' B O;,Me(F) ternary system formed from the binary phosphoric anhydride-fluoride system with an addition of boron oxide as a new component, a glass forming region is ex-' tended as shown in FIG. 1. In the accompanying Figures, Me(F) represents a mixture consisting of metal fluorides such as NaF, AlF MgF BaF and CaF in an appropriate ratio, and the term a perfectly stable glass forming region means such that 100 cc. of the glass do not devitrify even by main- In order to improve the water-durability, there have been incorporated heretofore high electro-charge fluorides such as zirconium fluoride, rare earth metal fluorides, thorium fluoride. Such fluorides, however, all do not dissolve respec- -tively in the glass in a desired amount and have a detrimental effect on the stability of the glass with regard to devitrification. Contrasting with this, if some boron oxide is incorporutcd, for example, 20-30 cationic parts of /2 B 0 on the basis of 100 cationic parts of phophoric anhydride in the glass are incorporated, the stability and water-durability are remarkably enhanced, and further, boron oxide can be stably introduced up to an amount of 70 cationic parts. This can be seen from FIG. 1 in which the glass forming region is extended by the incorporation of boron oxide. Further, the incorporation of J/z B 0 has not a detrimental influence on optical indices.

The glass of the present invention has the basic composition, V2 P O /z Bio -Me(F), wherein by cationic percent P 0 is in the range of 15 to 40% and /2 B 0 is 0.5 to 21%,

B/P being lower than 0.7. Me(F) represents R'F (alkali metal fluorides such as NaF, KF, LiF and the like), R"F (alkaline earth metal fluoride such as MgF and BaF and CaF and MB. The range of the alkali metal fluoride is (L40% and that of AlF is lO-25%, above which ranges each can not be stably dissolved in the glass. With lower than 15% of phosphoric anhydride, the glass becomes unstable and with above Abbe's number is lowered so that preferably optical properties can not be obtained. If boron oxide is lower than 0.5%, the aforementioned effect can not obtained, while if it higher than 21%, the glass is unstable. Further, the alkaline earth metal fluorides consist of three components, MgF CaF and BaF and the total of them should be l0-60%. If it is higher than 60%, the stability of the glass with respect to devitrification is BaF poor and lower than 10% do not give preferably optical indices to the glass because of the reduction of Abbe's number. The compositional ratio of MgF CaF and BaF depends on mainly an amount of phosphoric anhydride. For example, in the case of 20% /2 P 0 10% of NaF and 17.5% AlF the region defined by l040% MgF 20-50% BaF and 30-60% CaF wherein the calculation is carried out as the total of those divalent components is 100%, is capable of producing a stable glass, as shown in FIG. 2. Alternatively, in the case of 35% /2 P 0 10% NaF and 20% AlF the region defined by 045% MgF 30-90% BaF and 10-60% CaF is capable of producing a stable glass. Thus, the contents of alkaline earth metal fluorides should be in the range defined by the following 1 equations respectively:

MgF,

CaF

wherein P is an amount by cationic percent of phosphoric anhydride. A portion-of these RF components may be replaced by otherR 'F V m The present invention will be explained with respect to the following example in which the content of each component is Each glass composition as indicated in the following Table was prepared and mixed. The mixture was charged in a platinum crucible having a capacity of 800 cc. and heated at a temperature of about l,000 C to be fully vitrified. Then, the temperature was lowered to 900850 C. After stirring for 20 minutes, the melt was refined for 60 minutes and then again stirred for 10 minutes. Thereafter, with stirring, the temperature was lowered to 650 C and the melt was poured into a metal mold. In the Table, Glass No. 1 represents a contrast.

Glass numberr.

Composition:

001000001 ta e1 Cir-N h wwo A cocoouamgsjm oooooolnr- P] H H v-1 V2P205.... %B203 NaF llgFz. BBF2 C3Fz c vd. Water durability (boiling loss). Average crack length by 90.3 50.3 H. M A

Vickers Hardness Tester- 2. A stable fluoro-phosphate optical glass according to claim 1 in which said alkali metal fluoride is selected from a group consisting of lithium fluoride, sodium fluoride and potassium fluoride.

3. A stable fluoro-phosphate optical glass according to claim 1 in which said alkaline earth metal fluoride is selected from a group consisting of magnesium fluoride, barium 21 9x121; 9dl9ll1fl99l- I 4. A stable fluoro-phosphate optical glass according to claim 3 in which said alkaline earth metal fluorides are in the following ranges by cationic percent respectively, when calculated as MgF BaF CaF where P represents an amount of phosphoric anhydride by cationic percent. i l 

2. A stable fluoro-phosphate optical glass according to claim 1 in which said alkali metal fluoride is selected from a group consisting of lithium fluoride, sodium fluoride and potassium fluoride.
 3. A stable fluoro-phosphate optical glass according to claim 1 in which said alkaline earth metal fluoride is selected from a group consisting of magnesium fluoride, barium fluoride and calcium fluoride.
 4. A stable fluoro-phosphate optical glass according to claim 3 in which said alkaline earth metal fluorides are in the following ranges by cationic percent respectively, when calculated as MgF2 + BaF2 + CaF2 100%: MgF2 13- 2/3 (P- 15) * 45% BaF2 17+ 2/3 (P- 15) * 40++ 2 (P-15)% CaF2 37- 4/3 (P- 15) * 60 % where P represents an amount of phosphoric anhydride by cationic percent. 